The present invention relates to shock and vibration mounts, such as are used for mounting a supported device, e.g. a piece of electronic equipment, to a supporting surface, e.g. a frame or rack.
In principle, most shock and vibration mounts represent springs assigned to flex in every direction. With the nominal load "W" and the natural frequency "f.sub.m " given, the static deflection .delta..sub.n results according to the equation: ##EQU1## where "g" is the earth acceleration.
The maximal expected acceleration ("g") is indicated as "i". Hence the energy "Q" to be stored by the mount becomes a specified magnitude, calculated by the equation: ##EQU2## On the other hand the net material volume V of every spring is ##EQU3## where: "a" is a constant of the spring configuration. E is the elastic modulus, and
.SIGMA. is the max stress.
In pure shear, the elastomers of today allow the smallest material volume (V) of eq. (3), due to the low shear modulus and an a=2, the minimal possible constant.
In practice, it is desirable to reduce the volume (V) of the mount in order to minimize the space which must be left free for the mounts. It is particularly desirable that the mount have a profile which is as low as possible, since in most applications the height of the mount is a critical factor in determining the amount of "idle space" which must be made available in order to accomodate the mounts. Another desirable characteristics of such mounts is that they possess a low natural frequency, i.e., a large static deflection (.delta..sub.n) per equation (1). This is because the maximal expected ecceleration load at the lower frequencies are generally lower due to the fact that the frequency appears in the second power in the following equation: ##EQU4## wherein "A" is the vibrational amplitude. Because of the low shear modulus (E) in the shear mode, the static deflection (.delta..sub.n) will be higher per the following equation: ##EQU5## "H" is the height of the mount, "W" is the supported weight; and "S" is the strained area of the elastomer.
With a lower natural frequency (.phi..sub.m) the shock transmissability is also reduced.
Further desirable characteristics of such mounts is that they should flex equally in all directions, and that they should never "bottom". That is, even if loaded beyond the maximum, the deflecting member should never effect a metal contact; rather it should stiffen gradually to prevent excessive deflections.
An object of the present invention is to provide a shock and vibration mount having advantages in some or all of the above respects.